title: Insulin-like growth factor-I receptor internalization regulates signaling via the Shc/mitogen-activated protein kinase pathway, but not the insulin receptor substrate-1 pathway.
abstract: Insulin-like growth factor-I (IGF-I) receptors activate divergent signaling pathways by phosphorylating multiple cellular proteins, including insulin receptor substrate-1 (IRS-1) and the Shc proteins. Following hormone binding, IGF-I receptors cluster into clathrin-coated pits and are internalized via an endocytotic mechanism. This study investigates the relationship between IGF-I receptor internalization and signaling via IRS-1 and Shc. A mutation in the C terminus of the IGF-I receptor decreased both the rate of receptor internalization and IGF-I-stimulated Shc phosphorylation by more than 50%, but did not affect IRS-1 phosphorylation. Low temperature (15 degrees C) decreased IGF-I receptor internalization and completely inhibited Shc phosphorylation. Although receptor and IRS-1 phosphorylation were decreased in accordance with delayed binding kinetics at 15 degrees C, the ratio of IRS-1 to receptor phosphorylation was increased more than 2-fold. Dansylcadaverine decreased receptor internalization and Shc phosphorylation, but did not change receptor or IRS-1 phosphorylation. Consistent with these findings, dansylcadaverine inhibited IGF-I-stimulated Shc-Grb2 association, mitogen-activated protein kinase phosphorylation, and p90 ribosomal S6 kinase activation, but did not affect the association of phosphatidylinositide 3-kinase with IRS-1 or activation of p70 S6 kinase. These data support the concept that Shc/mitogen-activated protein kinase pathway activation requires IGF-I receptor internalization, whereas the IRS-1 pathway is activated by both cell surface and endosomal receptors.
authors.affiliation: Joslin Diabetes Center, Harvard Medical School, Boston, Massachusetts 02215, USA.
authors.forename: J C
authors.initials: JC
authors.lastname: Chow
authors.forename: G
authors.initials: G
authors.lastname: Condorelli
authors.forename: R J
authors.initials: RJ
authors.lastname: Smith
mesh_terms: D000818:Animals; D016466:CHO Cells; D002103:Cadaverine / Q000031:analogs & derivatives / Q000494:pharmacology; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism*; D002738:Chloroquine / Q000494:pharmacology; D006224:Cricetinae; D004705:Endocytosis; D006801:Humans; D055504:Insulin Receptor Substrate Proteins; D007334:Insulin-Like Growth Factor I / Q000378:metabolism; D007700:Kinetics; D008024:Ligands; D016297:Mutagenesis, Site-Directed; D010750:Phosphoproteins / Q000378:metabolism*; D010766:Phosphorylation; D017451:Receptors, Somatomedin / Q000235:genetics / Q000378:metabolism*; D011994:Recombinant Proteins / Q000378:metabolism; D015398:Signal Transduction; D014443:Tyrosine / Q000378:metabolism
chemical_list: C526292:IRS1 protein, human; D055504:Insulin Receptor Substrate Proteins; D008024:Ligands; D010750:Phosphoproteins; D017451:Receptors, Somatomedin; D011994:Recombinant Proteins; D014443:Tyrosine; D007334:Insulin-Like Growth Factor I; D002738:Chloroquine; D017871:Calcium-Calmodulin-Dependent Protein Kinases; C008542:monodansylcadaverine; D002103:Cadaverine